If it hasn't got Victa cast on the front top case ,then it could be for another mower manufacture like HG Palmer etc.
I'm not sure exactly what this number is from the 1 BAA 397 , After around 360,000 they started with a prefix letter A then later ones I think I've seen were BAA then BAB BAC BAD then went to C.
I've never tried to make a list of all the Victa numbers with a prefix letter but it could also possibly be for a boat motor or edger or fire fighting equipment as there were lots of other equipment that used the Victa 125 motor.
The Victa model 8 ,I've seen a few without Victa on the top case and some say they are original like that.